fn main() {
    let an_integer = 1u32;
    let a_boolean = true;
    let unit = ();
    let copied_integer = an_integer;
    println!("An Integer :{:?}", copied_integer);
    println!("A boolean :{:?}", a_boolean);
    println!("Meet the unit value:{:?}", unit);
    let _unused_variable = 3u32;
    let _noisy_unused_variable = 2u32;
    // 变量默认不可变，如果可变需要mut

    let _immutable_binding = 1;
    let mut mutable_binding = 1;
    println!("Before mutation:{}", mutable_binding);
    mutable_binding = 2;

    println!("After mutation:{}", mutable_binding);
    // 这行就错的，不能给不可变的变量赋值
    // _immutable_binding += 7;
}
